The present invention relates generally to a rivet which can be easily installed blind (from one side) and obtain both high shear and high tensile strengths; this is accomplished by a unique method of forming the upset head thereof.
Previous blind fastening systems incorporate a shaft or pin through the center of the fastener, which when pulled or in some instances driven inward upsets the end of the fastener on the inaccessible side or contains an explosive which upsets the blind head. Prior art has several shortcomings. First the pull-through or driven pin rivets are not suitable for pressure vessel applications since the pin hole penetrates completely through the shank, thus such rivets are not pressure tight. With the pull-through rivet the pin not only forms the head but deforms the body in order to fill the hole. The magnitude of these deformations is controlled by the tensile strength of the shaft or of a torque sensing driver or by the explosive charge all of which devices do not allow good quality control. The fasteners are heavier than conventional rivets or threaded tapered pins or bolts. These fasteners usually protrude into the hole further than conventional attachments due to the material required for the enlarged pin end and deformed head, which can create clearance problems as well as an associated weight penalty. The external head of the pull-through rivet is usually coarse and rough due to the broken pulled shaft. These fasteners are characterized by low strength and high cost due to the poor control of the forming process and excess material and components. There is therefore a definite need for a blind rivet with positive control of the forming of the blind head that does not have a hole completely through the shank.
Accordingly, it is an object of the present invention to provide a new and improved blind rivet for fastening two or more members.
Another object of the invention is to provide a strong fastener for both tensile and shear loads.
Another object of the invention is to provide a leak-free rivet.
Another object of the invention is to provide consistant head forming, a snug shank fit in the hole, and a tight fit between the rivet heads and the members being joined.
An additional object of the present invention is to retain all forces required to form the blind head within the rivet and a riveting tool instead of in the members being joined.
Still other objects of the present invention are to provide a low weight and low cost rivet that has a smooth exposed head after installation.
The foregoing and other objects of the present invention are attained by a unique method of upsetting the blind head. The upsetting is accomplished by plastically deforming a ductile material, such as soft aluminum, contained within a cavity by mechanically induced pressure. The ductile material is compressed by a force applied to a drive pin which protrudes from the preformed head prior to installation. The compression of the material within the cavity provided in the closed tubular end of the rivet generates a uniform internal pressure. This pressure will cause the blind head of the rivet to yield at the region of highest stress. This region is controlled by selectively thinning the walls of the cavity provided within the closed tubular end of the rivet. This end of the rivet is also annealed to foster plastic deformation. The total deformation of the blind head is controlled by the volume of the protruding part of the pin. When the pin is driven flush with the surface of the preformed head the upset head is completely formed.
The addition of a collar between the blind head and the members being joined provides increased tensile strength because of the improved support for the loaded side of the blind head.
An integrally formed hollow headed pin on the preformed head enables use of a riveting tool that forms the blind head without applying force to the members being joined. This feature is particularly suited to joining thin members not capable of supporting the driven pin forces that normally occur for rivets without the preformed headed pin. After riveting the preformed headed pin may be removed to provide a smooth or flush rivet head.